What's he thinking?!

I've been with my boyfriend for just over a year now (I'm 28 and he's 42). We've had ups and downs but things have been good. He's very stressed with work issues and on Friday night we had a small argument just before going to bed but it was forgotten in the morning. We pretty much live together (no big official moving in but he stays at my house every night and contributes to the rent).

On Saturday I was out with my friends and he'd had a bad day with work. He rang me in the afternoon and said he was stressed and fed up and I said if he wanted to come and meet us for some food to take his mind off stuff. He said no but for me to stay out as he knew I'd been down too and my friends would cheer me up as he wasn't in a mood for socialising. Fair enough we all get days like that. I went home at about 10pm and he was at home watching tv on the sofa.

I don't know why I did it and I know I shouldn't but just before we went to bed he'd been on facebook and I stupidly looked at his messages. He'd been chatting to his friend and they'd asked about me and him (a friend I haven't met they used to work together). He replied that he "wasn't sure", they asked why and he said "I just don't know if it feels right, I can't put my finger on it". I know he isn't cheating, the friend did say after "lol are you bored of just the one girl and want another" and he replied "No, not going down that road! I don't know...". I got a bit upset but looking at fb messages isn't something I'd normally do and I didn' know what to say.

I went to bed and sat straight up and just asked him if he was happy. He asked where it had come from and I said I just want to know, I don't want you be unhappy with me and I see so many of my friends relationships breaks down that I just want to check we're ok as we don't often talk about it. He said he was happy and content and that I shouldn't let my friends problems bring me down. I said I sometimes needed reassurance from him and he said he tries but he finds it v hard to talk about his feelings (I know this is true). I asked him straight out if he thought he loved me. He said "you know I love you" and I then cried and said "no I don't that's the problem. I need you to tell me sometimes". He said he didn't understand why I was getting so upset and how had this all come from nothing. He said how he gives me everything, he spends all his spare time with me, what more did I want from him that he wasn't giving? I cried a bit more and just said I don't want you to do more, I just want to know that you're happy! He said he was. We went to sleep in a bit of a mood with each other but woke up and made up this morning. I said sorry for going off at him and he said I was silly for thinking he doesn't want to be with me. He's nipped back to his this afternoon and text me again saying he's happy with me.

So now I'm just massively confused. Maybe he doesn't want t tell me there's a problem, or maybe he didn't want to appear soppy to his friend or maybe I should just run away as fast as I can. I've got no idea. I know I've had times where I've text friends after we've had an argument and said in the heat of the moment that maybe things weren't right and I'd hate for him to see those text messages!!
Yes, I know, this is what comes from snooping. Just wondered if anyone had any advice.